In some electrical systems, particularly sensitive electrical instrumentation and diagnostic systems, electrical grounding is difficult without introducing electrical noise into the system. If individual portions of the sensitive electrical instrumentation and diagnostic system are grounded at physically different points, so-called ground loops exist. Rapidly changing electromagnetic fields present near the sensitive electrical instrumentation couple the ground loops and can momentarily elevate different portions of the grounded circuit to different electrical potentials, thereby introducing electrical noise into the sensitive electrical instrumentation and degrading measurement sensitivity and accuracy.
A known solution to the problem caused by ground loops is to insure that all portions of the sensitive electrical instrumentation are grounded at a single common point. While establishing such a single-point ground is simple in concept, it is difficult in practice particularly where many test devices of a test system are powered from separate AC power lines, or where many data signal lines are applied to the electrical instrumentation system. In addition, since such sensitive electrical instrumentation is often enclosed within a grounded electromagnetic interference shielded enclosure or screen room, the potential for establishing ground paths other than the desired single-point ground is increased. If an electrical instrumentation system is enclosed in a grounded electromagnetic interference shielding enclosure and requires tens or hundreds of electrical connections prior to operation, the existence of a single undesired ground point can greatly affect measurements. Such undesired ground paths may also be introduced when the electrical instrumentation system is assembled or expanded.